Injection device

ABSTRACT

An injection device comprising an outer housing inside which is located a medicament-holding barrel with a needle at one end thereof, at least part of the needle being moveable in and out of the outer housing, a plunger moveable within the barrel, an inner housing intermediate the outer housing and the barrel and plunger and an energy source in communication with said inner housing. The inner housing is moveable by the energy source between a first position in which the plunger and barrel are movable axially so as to move at least part of said needle out of the outer housing; a second position in which the plunger is movable axially into said barrel so as to expel medicament through the needle; and a third position in which the plunger and barrel are able to retract in order to retract the needle into the outer housing.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/597,379, filed Jul. 21, 2006, which is a national stage applicationunder 35 U.S.C. 371 of PCT Application No. PCT/GB2005/000223 having aninternational filing date of Jan. 24, 2005, which designated the UnitedStates, which PCT application claimed the benefit of United KingdomApplication Serial No. 0401469.2, filed Jan. 23, 2004; CanadaApplication Serial No. 2,455,937, filed Jan. 27, 2004; and U.S. patentapplication Ser. No. 10/767,860, filed Jan. 28, 2004, the entiredisclosures of which are hereby incorporated herein by reference.

This invention relates to the field of injection devices for theadministration of liquid medication, for example, insulin or growthhormone.

One type of injection device is known as a mini-needle or micro-needledevice. These devices comprise a pressurised (“forced”) injection systemand have a needle which is shorter than that of conventional needlesystems. The needle is normally hidden which is advantageous both foravoiding needle stick injuries and for minimising trauma toneedle-phobic patients. The needle is hidden both before and after theinjection is delivered, appearing only for the duration of theinjection. Mini needle devices can typically deliver a larger volume ofmedication than needle-free devices and can deliver faster thanconventional needle systems.

One such known device is described in WO00/09186 (Medi-Ject Corporation)for “Needle assisted jet injector” and this document gives a usefulsummary of prior art devices.

The device of WO 00/09186 includes a needle which is, in one embodiment,retractably located within an injector nozzle assembly. Upon activationof a force generating source, a portion of the needle extends past thenozzle assembly and penetrates the outer layer of skin to delivermedicament via jet injection to a deeper region. After activation, theneedle retracts back into the nozzle assembly. The retractable needle ishoused within the nozzle and is pushed forward so that it emerges inorder to deliver an injection by the liquid medicament itself, when themedicament is itself pushed forward by the plunger.

Although the present invention may relate to mini-needle or jetinjection devices, the invention is equally applicable to other types ofinjection device, for example those for deep-penetrating muscularinjection as well as those which are for shallower, subcutaneous,injection.

According to a first aspect of the present invention there is providedan injection device comprising an outer housing inside which is located

-   -   a barrel for holding a volume of a medicament;    -   a needle at one end of the barrel, the needle and barrel being        such that at least part of the needle is axially moveable in and        out of said outer housing but is biased to be normally wholly        inside said housing;    -   a plunger, axially moveable within the barrel;    -   an inner housing intermediate the outer housing and the barrel        and plunger; and    -   an energy source in communication with said inner housing,        wherein the inner housing is moveable by the energy source        between three positions, namely    -   a first position in which the inner housing is in communication        with both the plunger and the barrel such that, in use, the        plunger and barrel are movable axially so as to move at least        part of said needle out of the outer housing;    -   a second position in which the inner housing is in communication        with the plunger but not the barrel such that, in use, said        plunger is movable axially into said barrel so as to expel        medicament through the needle; and    -   a third position in which the inner housing is in communication        with neither the plunger nor the barrel such that, in use, the        plunger and barrel are able to retract in order to retract the        needle into the outer housing.

The injection device according to the present invention provides asimple and cost-effective means of delivering medicament through aretractable needle. If desired, the device is able to deliver medicamentto a depth beyond the length of the needle because of the propulsiveforce provided by the energy source. As mentioned above, the injectiondevice is equally suitable for needle-assisted jet injection (deliveringmedicament to a depth beyond the length of the needle), conventionalinjection (to the depth of the needle penetration), or even to auser-adjustable needle penetration depth.

The device requires that the needle (and hence also the barrel to whichit is normally fixed) is moved axially so that the needle can appearbeyond the end of the nozzle for the duration of the injection, afterwhich the needle retracts automatically, out of sight of the user. Thedevice also requires that the plunger is moved axially (into the barrel)so that medicament is ejected. The overall complexity of the injectiondevice is significantly reduced by both of these requirements beingeffected by one component, namely the inner housing.

Preferably, said inner housing includes one or more radially flexibletags, each preferably located at the end of a resiliently flexible leg.

Preferably, one or more of said tags are situated at the rear end of theinner housing and are moveable radially into and out of communicationwith the plunger. In one embodiment, the tags are biased radiallyinwardly into communication with the plunger, preferably bycommunication with the outer housing. Alternatively, the tags are storedin their relaxed condition, before an injection is initiated.

Each rear tag may be moveable out of communication with the plunger whenaligned with a corresponding recess in the outer housing. Preferably,each rear tag is substantially T-shaped. One leg of the T-shape enablesthe rear tag to hook over the plunger and, effectively, pull the plungerforward (in the first and second positions mentioned above). The otherleg of the T-shape enables the rear tag to move radially outwardly tocatch in a recess in the housing (in the third position mentionedabove).

Preferably, one or more of said tags are situated at the forward end ofthe inner housing and are moveable radially into and out ofcommunication with the barrel. In one embodiment, the forward tags arebiased radially inwardly into communication with the barrel, preferablyby communication with the outer housing. Alternatively, the forward tagsare stored in their relaxed condition, before initiating an injection.

Each forward tag may be moveable out of communication with the barrelwhen aligned with a corresponding recess in the outer housing.Preferably, each rear tag is substantially L-shaped.

In a preferred embodiment, said energy source is a compressed gas.Alternatively, said energy source is a spring.

Preferably, the injection device further includes means for allowing theinner housing to move axially only forward with respect to the outerhousing. Ideally, said means is an arrangement of serrations, barbs,ratchet teeth or the like intermediate the housings.

Preferably, the injection device further comprises guide means forguiding, in use, the relative axial movement of the inner and outerhousings, the guide means preferably comprising one or more protrusionson said inner housing which, in use, cooperate with correspondingrecesses on an interior surface of said outer housing.

Preferably, said needle is biased to be normally wholly inside saidhousing by means of a spring intermediate the barrel and the outerhousing.

In one embodiment, the needle is removable from the device, this beingof benefit in applications where the device is reusable (for example ifa multiple-use cartridge of medicament is utilised).

In a further embodiment, said needle, barrel and plunger are removablefrom said device. It is intended that the device of the presentinvention could be constructed around a standard needle, barrel andplunger of known type.

Preferably, the injection device further includes a removable needlecover which protects the needle during storage and before use.Advantageously, said needle cover includes means for pulling aprotective rubber sheath or the like from said needle when said needlecover is removed from the device. Said pulling means may include afloating rivet intermediate the needle cover and the protective rubbersheath or the like, whereby twisting forces applied to said needle coverare substantially prevented from being transmitted to said rubber sheathor the like.

Preferably, the presence of said needle cover on said device serves as asafety lock, substantially preventing relative forward movement of saidouter housing.

In a preferred form, the injection device further comprises a viewingwindow in said barrel aligned with a viewing window in said outerhousing such that said medicament can be viewed by a user prior to aninjection taking place. Preferably, in use during an injection, saidinner housing moves intermediate said viewing window in the outerhousing and said barrel so as to obscure the window in the barrel fromthe user's view.

Preferably, the injection device includes means for emitting an audibleand/or physical indication to a user that the injection is complete.

According to a second aspect of the invention there is provided aninjection device comprising an outer housing inside which is located

-   -   a barrel for holding a volume of a medicament;    -   a needle at one end of the barrel, the needle and barrel being        such that at least part of the needle is axially moveable in and        out of said outer housing but is biased to be normally wholly        inside said housing;    -   a plunger, axially moveable within the barrel;    -   an inner housing intermediate the outer housing and the barrel        and plunger; and    -   an energy source in communication with said inner housing,    -   wherein the inner housing is moveable by the energy source        between two positions, namely    -   a first position in which the inner housing is in communication        with the plunger but not the barrel such that, in use, said        plunger is movable axially into said barrel so as to expel        medicament through the needle; and    -   a second position in which the inner housing is in communication        with neither the plunger nor the barrel such that, in use, the        plunger and barrel are able to retract in order to retract the        needle into the outer housing.

According to a third aspect of the invention there is provided aninjection device comprising an outer housing adapted to receive:

-   -   a barrel for holding a volume of a medicament;    -   a needle at one end of the barrel, the needle and barrel being        such that at least part of the needle is axially moveable in and        out of said outer housing but is biased to be normally wholly        inside said housing; and    -   a plunger, axially moveable within the barrel,    -   characterised in that the injection device further comprises:

an inner housing intermediate the outer housing and the barrel andplunger; and

-   -   an energy source in communication with said inner housing,    -   wherein the inner housing is moveable by the energy source        between three positions, namely    -   a first position in which the inner housing is in communication        with both the plunger and the barrel such that, in use, the        plunger and barrel are movable axially so as to move at least        part of said needle out of the outer housing;    -   a second position in which the inner housing is in communication        with the plunger but not the barrel such that, in use, said        plunger is movable axially into said barrel so as to expel        medicament through the needle; and    -   a third position in which the inner housing is in communication        with neither the plunger nor the barrel such that, in use, the        plunger and barrel are able to retract in order to retract the        needle into the outer housing.

Preferred embodiments of the present invention will now be moreparticularly described, by way of example only, with reference to theaccompanying drawings wherein:

FIG. 1 is a perspective view, partly in section, showing the injectiondevice, in the condition in which it is supplied to a user, apart fromthe needle cover;

FIG. 2, drawn to a larger scale, shows detail of part of the deviceshown in FIG. 1;

FIG. 3 is a perspective view, partly in section, showing the injectiondevice, during an injection;

FIG. 4, drawn to a larger scale, shows detail of part of the deviceshown in FIG. 3;

FIG. 5 is a perspective view, partly in section, showing the injectiondevice, with the plunger fully depressed into the barrel;

FIG. 6, drawn to a larger scale, shows detail of part of the deviceshown in FIG. 5;

FIG. 7 is a perspective view, partly in section, showing the injectiondevice, after use and safe to dispose of;

FIG. 8, drawn to a larger scale, shows detail of part of the deviceshown in FIG. 7;

FIG. 9 is a perspective view of the device, including the needle cover;

FIG. 10 is perspective view, partly in section, showing detail of theneedle cover;

FIG. 11 is perspective view, partly in section, showing detail of theneedle cover part way through being removed from the injection device;

FIG. 12 is a schematic view showing the relationship between tags 7A andram 4, in one embodiment of the invention;

FIG. 13 is a perspective view of the inner housing (also referred to asthe “plunger housing”);

FIG. 14 is a side view of the inner housing of FIG. 13;

FIG. 15 is a perspective view, partly in section, showing an alternativeembodiment of the injection device, in the condition in which it issupplied to a user;

FIG. 16, drawn to a larger scale, shows detail of the rear end of thedevice shown in FIG. 15;

FIG. 17 shows detail of the interaction between the spring housing 41and the rear of the outer housing 30;

FIG. 18 is a perspective view, partly in section, showing the injectiondevice with the needle cover removed, immediately prior to initiating aninjection;

FIG. 19 is a perspective view, partly in section and drawn to a largerscale, showing the front part of the device immediately beforeinitiating an injection;

FIG. 20 is a perspective view, partly in section, showing the front partof the device at the start of an injection;

FIG. 21 is a perspective view showing the device in the same conditionas FIG. 20, i.e. at the start of an injection with the needle emergingfrom the end of the device and the plunger beginning to travel down thebarrel;

FIG. 22 is a perspective view, partly in section, showing the injectiondevice with the plunger fully depressed into the barrel;

FIG. 23 is a perspective view, partly in section, showing the injectiondevice after use and with the needle retracted into the device;

FIG. 24 is a perspective view of the assembled device, including theneedle cover;

FIG. 25 is a schematic view of part of the front end of the device,showing the helical protrusion on the nozzle.

FIG. 26 is perspective view, partly in section, showing detail of theneedle cover; and

FIG. 27 is perspective view, partly in section, showing detail of theneedle cover after removal from the device.

Throughout the following description, reference to a “forward” directionmeans the direction which is towards the patient when the injectiondevice is in use. The “forward” end of the injection device is the endnearest the patient's skin when the device is in use. Similarly,reference to a “rearward” direction means the direction which is awayfrom the patient and the “rearward” end of the device is the endfurthest from the patient's skin when the injection device is in use.

FIG. 1 is a perspective view, partly in section, showing the injectiondevice, in the condition in which it is supplied to a user, apart fromthe needle cover (which is described below after describing the mainoperation of the device).

The principal components of the device will now be described withreference to FIGS. 1 and 2. An energy source 1 is provided at the rearof the device which, in this embodiment, is a gas cylinder similar tothe type used in a conventional aerosol can or the like i.e. having avalve through which gas can be released at will and in a controlledmanner. In an alternative embodiment of the invention, a spring is usedas the energy source in place of a gas cylinder and this embodiment isdescribed later with reference to FIG. 13 et seq.

The valve 2 of the gas cylinder opens into a chamber 3, which in FIG. 1is of relatively small volume. The front wall of the chamber 3 isdefined by a ram 4 which has an annular seal 5 at the rear thereof inorder to make the chamber 3 gas-tight. The rear wall of the chamber 3 isdefined by the back face of a generally cylindrical chamber housing 6.

The forward part of the ram 4 abuts or alternatively isintegrally-formed with an inner housing 7 which closely surrounds aplunger 8 (and can therefore be referred to as the “plunger housing”).The rear of the plunger housing includes four orthogonally placed tags7A, which each have a “hammer head” or T-shape and whose tendency tospring radially outwardly is restricted by the diameter of the chamberhousing 6. If the ram 4 is integrally formed with the plunger housing 7as illustrated in FIGS. 13 and 14, the tags 7A are positioned at the endof flexible legs cut into the housing, so that the tags 7A can moveradially, with respect to the ram 4 and remainder of housing 7.

The hammer head of each tag 7A hooks over the enlarged head 8A of theplunger 8, so that the tags 7A are in contact with the plunger head 8A,as shown best in FIG. 2.

The plunger 8 is the plunger of a syringe arrangement comprising abarrel 9 in which a predefined volume of liquid medicament is suppliedand a needle 10 through which the medicament can be delivered to thepatient. A nozzle 11 at the front end of the injection device normallyconceals the needle 10 from the user's view. A spring 12, positionedbetween the outer housing and the barrel 9 biases the needle to benormally wholly within the nozzle 11.

At the front end of the plunger housing 7, there are furtherorthogonally placed tags 7B, which each have a generally L shape andwhose tendency to spring radially outwardly is restricted by thediameter of the chamber housing 6. The tags 7B each abut the flange atthe rear of barrel 9.

Other means of interaction between the inner housing and the plunger maybe envisaged, instead of tags 7A, for example tags that are notT-shaped, or means that push the plunger rather than pulling as in thedescribed embodiment.

There are four main stages in the operation of the device. Stage 1 isthe condition shown in FIGS. 1 and 2, i.e. the device as supplied to auser, and as described above. The medicament is already present in thebarrel 9 and the needle 10 is concealed from view within the nozzle 11.The plunger 8 is fully withdrawn from the barrel 9 (because of theliquid medicament contained within the barrel) and the head of theplunger 8A abuts the tags 7A. The rear of the remainder of housing 7abuts the ram 4. The chamber 3 is of minimal volume.

Stage 2 of operation is the injection stage illustrated in FIGS. 3 and4. With the injection device held against the patient's skin at theinjection site, downward force is applied to the device in the directionindicated by the arrow F in FIG. 2. This force causes the valve of thegas cylinder 1 to open, releasing gas into the chamber 3. As the chamber3 fills with gas, the ram 4 is urged forward, consequently urging tags7A against the plunger 8. As the tags 7A, and hence the plunger housing7, are urged forward, the cooperation of the tags 7B against the barrel9 means that the barrel is also urged forward, against the bias of aspring 12 (shown in FIG. 3). As the barrel 9 moves forward, so does theneedle 10 which is attached thereto and so the needle protrudes out ofthe nozzle 11 sufficiently to enable an injection to be delivered.Therefore, initially, the ram 4 causes the plunger housing 7, theplunger 8, the barrel 9 and the needle 10 to move forwards.

Shortly after the plunger housing 7 starts to move forward, the tags 7Breach a lip in the chamber housing 6. The tags 7B spring radiallyoutwardly over this lip, as shown in FIGS. 3 and 4. Once the tags 7Bhave sprung outwardly in this way, they are no longer in abutment withthe barrel 9. This means that the barrel 9 (and hence needle 10) is nolonger urged forwards because the forwardly-moving plunger housing 7,including tags 7B, are free to continue moving forward withoutcontacting the barrel 9.

Therefore, once the device has reached the condition illustrated inFIGS. 3 and 4, continued forward movement of the ram 4 and plungerhousing 7 causes the plunger 8 to be urged forward into the barrel 9.This expels the liquid medicament from the barrel 9, through the needle10 to deliver an injection. It is the cooperation of the tags 7A withthe enlarged head 8A of the plunger which transmits the forward forcefrom the ram 4/housing 7 to the plunger 8.

The third stage in the operation of the device is illustrated in FIGS. 5and 6. When the plunger 8 is depressed into the barrel 9, the desireddose of medicament is delivered into the patient. At this point, thetags 7A reach recesses 13 cut into the plunger housing 6 whereupon theyare able to spring radially outwardly into those recesses (asillustrated in FIGS. 5 and 6). An audible click may be emitted whichindicates to the user that the injection is complete. In addition, theuser may “feel” that the injection is complete as a result of the tags7A locating in recesses 13.

The outward movement of the tags 7A means that the “hammer head” shapeis no longer in contact with the enlarged head 8A of the plunger 8 andtherefore the plunger 8 is no longer driven forward by the ram 4 andtags 7A. The plunger housing 7 may continue further forward until an endstop is reached.

The final stage in the operation of the device is illustrated in FIGS. 7and 8. With the tags 7A located within recesses 13, neither the plunger8 nor the barrel is impeded by any part of the plunger housing 7.Therefore the spring 12, which had been compressed by the forward motionof the barrel 9, urges the barrel 9 and hence the plunger 8 backwardsuntil the ram 4 prevents further backward movement thereof. The backwardmovement is sufficient to cause the needle 10 to retract into the nozzle11 so that it is no longer visible to the user and safe from the risk ofcausing a needle-stick injury. The used injection device can then besafely disposed of.

Blow-back is prevented by the provision of serrations 14 which guide therelative movement of the chamber housing and the outermost housing.These serrations only permit relative movement in one direction, i.e.the chamber housing 6 moving forward with respect to the outermosthousing.

FIG. 9 is a perspective view of the injection device which, in thisFigure, includes a needle cover 15. The needle cover is shown in furtherdetail in FIGS. 10 and 11 and is used to protect the needle end of theinjection device during transit, storage and before use to deliver aninjection. The needle cover 15 has the further advantage of preventingaccidental or unintended activation of the device, as it is not possibleto fire the device with the needle cover 15 in place.

Regulations require that the needle (which is in direct communicationwith the medicament in the barrel) is sealed from the outsideenvironment before use. This is achieved by providing protection in theform of a rubber moulding 16 which covers the end of the needle, therubber moulding 16 being surrounded by a nylon sheath 17. The rubbermoulding and nylon sheath (the “needle protection”) are fixed withrespect to one another by a friction fit between one or more protrusions16A on the rubber moulding and a corresponding one or more recesses 17Ain the nylon sheath.

The configuration of the needle protection depends upon the type ofneedle/barrel/plunger (“syringe assembly”) employed in the injectiondevice. It is envisaged that the injection device of the presentinvention could be assembled around a standard syringe assembly of knowntype (the selection thereof depending upon the required dose range, thetype of medicament to be administered etc, for example). Differentsyringe assemblies may be supplied with slightly differing needleprotection.

The nylon sheath and rubber moulding are firmly fixed on the needle 10and it is difficult, if not impossible, for a patient to pull them fromthe needle using his/her fingers alone because of their position insidethe nozzle 11. Therefore an outer needle cover 15 is provided which notonly improves the aesthetic appearance of the injection device, beforeuse, but also serves the function of facilitating the removal of thenylon sheath and rubber moulding.

The needle cover 15 is releasably retained on the front end of theinjection device by the fit of annular protrusions 18 on part of thedevice housing with grooves 19 on the interior of the needle cover. Theprotrusions 18 and corresponding grooves 19 preferably extend around twoequally opposed 60° portions of the circumference of the nozzle 11.

The grooves 19 are located on one or more (preferably equally spaced)flexible legs 20 which are flexible compared to the rest of the needlecover 15, about point P shown in FIG. 9. Forward of each groove 19 isprovided an inwardly projecting tab 21 on each flexible leg 20. Each tab21 abuts the rear of the nylon sheath 17.

Turning now to FIG. 11, when it is desired to remove the needle cover 15from the device, the user grips the needle cover, preferably in a regionhaving texture or other grip-improving means 22, and pulls in thedirection indicated by the arrow in FIG. 11. The flexibility of the legs20 permits the needle cover to ride over the protrusions 18, disengagingthem from the grooves 19. The flexibility of the legs 20 is minimalenough not to cause the tabs 21 to become disengaged from the rear ofthe nylon sheath 17.

Therefore, as the needle cover 15 is pulled in the direction indicatedby the arrow, the tabs 21 are urged against the rear of the nylon sheath17 and sufficient force can be applied thereby to disengage the needle10 from the rubber moulding 16. In this way, the entire moulding 16,nylon sheath 17 and needle cover 15 can be removed from the injectiondevice and discarded, so that the injection device is then ready to use.

Other types of needle cover 15 may be envisaged, suited to theparticular type of syringe assembly used in the device, for example thatdescribed below with reference to FIG. 25 et seq.

FIGS. 13 and 14 show more detail of an embodiment of the inner housing 7in which the ram 4 is integral with the housing 7.

The inner housing is injection moulded as a single piece having fourorthogonally placed tags at each end thereof. Each tag 7A, 7B is at theend of a resiliently flexible leg, cut out of the material of thehousing 7, so that each leg (and its respective tag) is able to flexradially with respect to the remainder of the housing 7.

The rear part of the inner housing 7 constitutes the equivalent of theram 4 described above. The ram is provided with an annular groove orrecess 4A, into which the ball bearings 42 locate.

The inner housing 7 may also be provided with one or more guide meanswhich, in the illustrated embodiment, take the form of elongateprotrusions 7C. These protrusions 7C cooperate with correspondingrecesses on the interior surface of the outer housing 30 so that, inuse, relative axial movement of the inner and outer housings is guided.

A spring-powered embodiment of the injection device is described belowwith reference to FIG. 15 et seq.

In this embodiment, there is a generally cylindrical outer housing 30extending all the way from the rear of the device to the needle cover15. The gas cylinder 1 and valve 2 are replaced by a spring-poweredenergy source. Referring particularly to FIG. 16, a spring 40 isprovided under compression at the rear of the device, intermediate therear of a spring housing 41 and the ram 4. The spring 40 is retained inits compressed condition by means of one or more ball bearings 42sitting in annular recess 4A on the ram 4, the ball bearings 42 beingwedged against the outer housing 30 and located in apertures 41C at thefront of the spring housing 41. The spring housing 41 interacts with theback of the outer housing 30 by means of an arrangement illustrated inFIG. 17.

The spring housing 41 is provided with elongate slots 41B and generallycircular apertures 41C. The corresponding part of the outer housing isprovided with elongate protrusions 30B on the interior surface thereof,which fit into the slots 41B as illustrated in FIG. 17. The ballbearings 42 (not shown in FIG. 17) fit through the circular apertures41C.

In FIG. 15 it can be seen that the front end of the outer housing 30 isin close relation, or abutting, the needle cover 15. This substantiallyprevents any forward movement of the outer housing 30 in relation to thespring housing 41 and other components.

In FIG. 18, the needle cover has been removed and it is now possible toplace the device against the user's leg (or other injection site) readyto initiate an injection. FIG. 19 shows the front part of the device atthis stage, in more detail.

Referring now to FIGS. 19 and 20, the front part of the device is shownin more detail. At the front of the outer housing 30, there are providedtwo annular grooves 30A and 30A′ on the interior surface thereof. Aspacer part 50 is fixed with respect to the nozzle 11 and othercomponents internal of the outer housing 30. The spacer part 50 isprovided with an exterior annular protrusion 51 which initially locatesin the forwardmost groove 30A.

The leading edge of forwardmost groove 30A is generally blunt so thatlocation of protrusion 51 therein (as illustrated in FIG. 19) inhibitsthe user from pulling the outer housing 30 rearwardly off the springhousing 41 et al, which might dangerously expose the internal componentsof the device. It is difficult for a user to apply sufficient rearwardforce to cause the protrusion 51 to ride over the blunt leading edge.

The trailing edge of the forwardmost groove 30A and both edges of thegroove 30A′ are curved or tapered.

To initiate an injection, the user grasps the outer housing 30 andeffects forward movement of the outer housing 30 in relation to thespring housing 41. As shown in FIG. 20, the forward movement causes theprotrusion 51 to disengage from the forwardmost groove 30A and, as theouter housing 30 moves forward with respect to the spacer 50, theprotrusion 51 engages in the rearmost groove 30A′.

Referring now to FIGS. 18 and 21, the relationship between the ram 4,ball bearings 42 and spring housing 41 is described in more detail. Inthe first position, shown in FIG. 18, the ball bearings 42 sit in theannular groove 4A in the ram 4 and are wedged in place in the apertures41C at the front of the spring housing 41.

FIG. 21 shows the device in the same condition as in FIG. 20 i.e.wherein forward movement of the outer housing in relation to the springhousing has caused the protrusion 51 to be engaged in the rearmostgroove 30A′.

In this position, the spring housing 41 has moved closer to the rear ofthe outer housing 30. This relative axial movement is sufficient tocause the apertures 41C to retreat back past an undercut area 30A″inside the outer housing 30. The ball bearings 42 are now free to moveradially out of the apertures 41C and into said undercut area 30A″, outof engagement with the ram 4. The ram 4 is now free to travel forwardsin the direction indicated by the arrow in FIG. 21, under the power ofthe spring 40.

The forward-moving ram 4 causes the inner housing 7 to deliver theinjection as previously described. This is illustrated in FIG. 21 (Stage2 as previously described) and FIG. 22 (Stage 3 as previouslydescribed).

FIG. 23 shows the position in which the injection has been fullydelivered and the needle caused to retract back inside the nozzle (finalstage as previously described).

In an alternative embodiment (not illustrated), the ball bearings 42 arereplaced by a living joint, moveable into undercut area 30A″ and out ofengagement with the ram 4.

In another embodiment (not illustrated), the protrusion 51 and grooves30A, 30A′ are replaced or supplemented by a ratchet arrangementdescribed hereafter. A spring housing is provided which has asubstantially square cross-section. A portion of the inside of the outerhousing 30 is correspondingly shaped with a square cross-section so thatthe spring housing and outer housing closely fit together but relativeaxial movement between them is possible. Relative rotational movementbetween them is substantially prevented by the square cross-section. Atleast one surface of the square cross-section spring housing is providedwith a plurality of barbs, protrusions, ratchet teeth or the like whichcooperate with an inwardly-depending protrusion or tag on the inside ofthe outer housing.

The ratchet arrangement performs the same function as protrusion 51 andgrooves 30A, 30A′ i.e. to control forward movement of the outer housing30 in relation to the spring housing 41. The ratchet arrangement mayprovide further advantages, for example:

-   -   Improved strength;    -   Rotational alignment between spring housing and outer housing;    -   Improved resistance to rearward force generated by the user        pushing the device hard into the injection site;    -   Improved resistance to the user pulling the outer housing        rearwardly off the device, the ratchet teeth permitting forward        movement of the outer housing only;    -   Improved defining of the relative axial position of the outer        housing and internal components of the device.

Alternative embodiments are envisaged in which, instead of a squarecross-section, the spring housing has at least one flat surface on whichthe barbs, protrusions, ratchet teeth or the like are disposed; theremainder of the spring housing may be of any cross-sectional shape solong as the inside of the outer housing is correspondingly shaped.

Other modifications to the injection device are illustrated in FIG. 13et seq which are equally applicable to the gas-powered embodimentdescribed earlier.

The barrel 9 may be provided with a transparent window 9 a which, inuse, is aligned with a window 32 in the outer housing (see FIG. 24) sothat the liquid medicament is visible. During the injection (i.e. duringfiring of the injection device), the plunger housing 7 becomes visibleas it moves forwardly intermediate the barrel 9 and outer housing. Asthe plunger housing 7 moves forwardly, it progressively obscures thewindow 9 a thus giving a visual indication to the user of the progressof the injection. The window 9 a may be completely obscured by theplunger housing 7 when the injection is complete. The plunger housing 7may be brightly coloured e.g. red to increase its visibility through thewindow 30.

It is observed that plastics of the type which may be used to form theplunger housing 7 will, over time, tend to gain a memory of the positionin which they are stored. It is essential for operation of the devicethat the tags 7A spring properly into and out of engagement with theenlarged head 8A of the plunger. Therefore, as visible in FIG. 18, atapered surface 31 is provided on the interior of the outer housing 30.This enables the tags 7A to be stored in their “relaxed” position, i.e.sprung radially-outwardly to abut the outer housing 30, as illustratedin FIG. 18.

When an injection is initiated as shown in FIG. 21, the forward movementof the outer housing 30 in relation to the plunger housing 7 causes thetags 7A to ride up the tapered surface 31 and into engagement with theenlarged head 8A of the plunger.

When the plunger housing 7 has moved forward sufficiently for tags 7A toreach recesses 13, the tags 7A will have an increased tendency to springoutwardly into the position in which they had been previously stored,ensuring efficient operation of the device.

FIGS. 26 and 27 show an alternative embodiment of the needle cover 15.Like parts are given the same reference numerals as in FIG. 11. In theFIG. 26 embodiment, the needle cover 15 is releasably retained on thefront end of the injection device by the fit of protrusions 11A on theexterior of the nozzle 11 with corresponding recesses on the interior ofthe needle cover 15.

The protrusions 11A may take the form of a single helical protrusion asillustrated in FIG. 25, or alternatively several discrete protrusionsmay be used.

At the front end of the needle cover 15 is a floating rivet 35 which hasrearwardly directed barbed fingers 36 which pass through an aperture inthe front end of the sheath 17.

The protrusions 11A the barbed fingers 36 and the interaction of thenozzle with the needle cover 15 at surface 15A mean that the nozzle 11and associated components are prevented from moving axially with respectto the housing 30 in the situation illustrated in FIG. 26. This meansthat the device cannot be inadvertently fired whilst the needle cover 15is still in place.

When it is desired to remove the needle cover 15 from the device, theuser grips the needle cover and pulls in the direction indicated by thearrow in FIG. 26, using a twisting motion to cause the needle cover toride along the nozzle guided by the helical protrusion 11A.

The floating rivet 35 allows the needle cover 15 to be twisted in orderfor it to move along helical protrusion 11A, but the sheath 17 does nottwist and is simply pulling axially off the needle. This means there isno risk of damage to the needle 10 caused by twisting forces.

As the needle cover 15 is pulled in the direction indicated by thearrow, the barbed fingers 36 pull the sheath 17 with sufficient force todisengage the needle 10 from the rubber moulding 16. In this way, theentire moulding 16, nylon sheath 17 and needle cover 15 can be removedfrom the injection device and discarded, so that the injection device isthen ready to use. Removal of the needle cover 15 has the secondfunction of allowing the nozzle etc to be free to move axially withrespect to the housing 30, which enables the device to be fired asdescribed above.

When the end of the protrusion 11A is reached, the needle cover 15 isdisengaged from the nozzle 11 as illustrated in FIG. 27.

A further embodiment of the present invention is envisaged wherein theneedle is exposed upon removal of the needle cover 15. Such anembodiment may be suitable for users where needle-phobia is not aconcern and where the complexity (and hence cost) of the device can bereduced by eliminating the need for the first stage (i.e. the forwardmovement of the needle out of the nozzle 11). The optional needle cover15 may be omitted from such an embodiment. As mentioned above, it ispossible that the injection device of the present invention may besupplied separately from and then assembled around a standard syringeassembly (needle/barrel/plunger) of known type.

In a further development, it is envisaged that it would be readilypossible to adapt the device of the present invention to be operablewith a standard cartridge or vial of medicament (containing a volume ofmedicament from which several doses of user-defined volume can beprovided) instead of a syringe assembly. In such case the needle couldbe removable and replaceable so that the device could be reused untilthe medicament cartridge is empty.

1. An injection device comprising an outer housing inside which islocated a barrel for holding a volume of a medicament; a needle at oneend of the barrel, the needle and barrel being such that at least partof the needle is axially moveable in and out of said outer housing butis biased to be normally wholly inside said housing; a plunger, axiallymoveable within the barrel; an inner housing intermediate the outerhousing and the barrel and plunger; and an energy source incommunication with said inner housing, Characterized in that the innerhousing is moveable by the energy source between three positions, namelya first position in which the inner housing has one or more readiallyflexible tags which are in communication with the barrel such that, inuse, the plunger and the barrel are movable axially so as to move atleast part of said needle out of the outer housing; a second position inwhich the inner housing has one or more radially flexible tags which arein communication with the plunger but not the barrel such that, in use,said plunger is movable axially into said barrel so as to expelmedicament through the needle; and a third position in which said one ormore radially flexible tags on the inner housing are in communicationwith neither the plunger nor the barrel such that, in use, the plungerand barrel are able to retract in order to retract the needle into theouter housing.
 2. An injection device as claimed in claim 1 furthercomprising a spring housing intermediate the outer housing and the innerhousing.
 3. An injection device as claimed in claim 1 wherein one ormore of said tags is located at the end of a resiliently flexible leg.4. An injection device as claimed in claim 1, wherein one or more ofsaid tags are situated at the rear end of the inner housing and aremoveable radially into and out of communication with the plunger.
 5. Aninjection device as claimed in claim 2, wherein said tags are biasedradially inwardly into communication with said plunger, preferably bycommunication with said spring housing.
 6. An injection device asclaimed in claim 1, wherein said tags are stored in their relaxedcondition, before initiating an injection.
 7. An injection device asclaimed in claim 2, wherein each rear tag is moveable out ofcommunication with the plunger when aligned with a corresponding recessin the spring housing.
 8. An injection device as claimed in claim 1,wherein each rear tag is substantially T-shaped.
 9. An injection deviceas claimed in claim 1, wherein one or more of said tags are situated atthe forward end of the inner housing and are moveable radially into andout of communication with the barrel, wherein said forward tags arebiased radially inwardly into communication with said barrel, preferablyby communication with said spring housing, wherein said forward tags arestored in their relaxed condition, before initiating an injection,wherein each forward tag is moveable out of communication with thebarrel when aligned with a corresponding recess in the outer housing,and wherein each forward tag is substantially L-shaped.
 10. An injectiondevice as claimed in claim 1, further including means for allowing theinner housing to move axially only forward with respect to the outerhousing, wherein said means is an arrangement of serrations, barbs,ratchet teeth or the like intermediate the housings.
 11. An injectiondevice as claimed in claim 1, further comprising guide means forguiding, in use, the relative axial movement of the spring and outerhousings, the guide means preferably comprising one or more protrusionson said spring housing which, in use, cooperate with correspondingrecesses on an interior surface of said outer housing.
 12. An injectiondevice as claimed in claim 1, wherein said needle is biased to benormally wholly inside said housing by means of a spring intermediatethe barrel and the outer and/or spring housing.
 13. An injection deviceas claimed in claim 1, further including a removable needle cover whichprotects the needle during storage before use, wherein said needle coverincludes means for pulling a protective rubber sheath or the like fromsaid needle when said needle cover is removed from the device, andwherein said pulling means includes a floating rivet intermediate theneedle cover and the protective rubber sheath or the like, wherebytwisting forces applied to said needle cover are substantially preventedfrom being transmitted to said rubber sheath or the like.
 14. Aninjection device as claimed in claim 13, wherein the presence of saidneedle cover on said device serves as a safety lock, substantiallypreventing relative forward movement of said outer housing.
 15. Aninjection device as claimed in claim 1, further comprising a viewingwindow in said barrel aligned with a viewing window in said outerhousing such that said medicament can be viewed by a user prior to aninjection taking place.
 16. An injection device as claimed in claim 15wherein, in use during an injection, said inner housing movesintermediate said viewing window in the outer housing and said barrel soas to obscure the window in the barrel from the user's view.
 17. Aninjection device as claimed in claim 1, further comprising means foremitting an audible and/or physical indication to a user that theinjection is complete.
 18. An injection device comprising an outerhousing inside which is located a barrel for holding a volume of amedicament; a needle at one end of the barrel, the needle and barrelbeing such that at least part of the needle is axially moveable in andout of said outer housing but is biased to be normally wholly insidesaid housing; a plunger, axially moveable within the barrel; an innerhousing intermediate the outer housing and the barrel and plunger; andan energy source in communication with said inner housing, characterizedin that the inner housing is moveable by the energy source between twopositions, namely a first position in which the inner housing has one ormore radially flexible tags which are in communication with the plungerbut not the barrel such that, in use, said plunger is movable axiallyinto said barrel so as to expel medicament through the needle; and asecond position in which said one or more radially flexible tags on theinner housing are in communication with neither the plunger nor thebarrel such that, in use, the plunger and barrel are able to retract inorder to retract the needle into the outer housing.
 19. An injectiondevice comprising an outer housing adapted to receive: a barrel forholding a volume of a medicament; a needle at one end of the barrel, theneedle and barrel being such that at least part of the needle is axiallymoveable in and out of said outer housing but is biased to be normallywholly inside said housing; and a plunger, axially moveable within thebarrel, wherein the injection device further comprises: an inner housingintermediate the outer housing and the barrel and plunger; and an energysource in communication with said inner housing, characterized in thatthe inner housing is moveable by the energy source between threepositions, namely a first position in which the inner housing has one ormore radially flexible tags in communication the barrel such that, inuse, the plunger and barrel are movable axially so as to move at leastpart of said needle out of the outer housing; a second position in whichthe inner housing has one or more radially flexible tags incommunication with the plunger but not the barrel such that, in use,said plunger is movable axially into said barrel so as to expelmedicament through the needle; and a third position in which the saidradially flexible tags on the inner housing are in communication withneither the plunger nor the barrel such that, in use, the plunger andbarrel are able to retract in order to retract the needle into the outerhousing.
 20. An injection device as claimed in claim 19 furthercomprising a spring housing intermediate the outer housing and thespring housing.